Pulse receiving system



c. w. HANsELL 2,424,274

PULSE RECEIVING SYSTEM July 22, 1947.

original Filed June 24, 1942 FRE'. M00.

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ATTORNEY Patented July 22, 1947 PULSE RECEIVING SYSTEM Clarence W. Hansell, Port Jefferson, N. Y., as-

signor to Radio Corporation of America, a corporation of Delaware Original application June 24, 1942, Serial No.

8 Claims.

The present invention relates to an improved earth signaling communication system employing electrical pulses, and is a division of my United States Patent 2,389,432, dated November 20, 1945.

Divided and 30, 1945, Serial No. 613

this application August ,512

The following is a more detailed description of the invention accompanied by a drawing, wherein:

Fig. 1 illustrates one pulse type transmitter in accordance with the invention, and

Briefly stated, the invention consists in the 5 Fig. 2 illustrates a pulse type receiving system use of very short high-power pulses delivered by for use with the transmitter of Fig. l. the transmitter to two spaced ground connec- Referring to Fig. l, I have shown a frequency tions, and likewise received by connecting a. remodulated pulse oscillator and amplifier comceiver between two spaced ground connections. lo prising double element vacuum tube amplier These ground connections may comprise two 2l. One part of tube 2l is provided with reground electrodes which can be inserted into the generative feed back transformer T2 and the earth a suitable distance apart, such as 100 feet time constant circuit made up of resistance R1 more or less. The effectiveness and range of and condenser C1. The resistance R2 and conthe system will, of course, vary with the disdenser C2 provide a grid bias to the control electance between the ground connections, and by trode of the oscillator part of tube 2i and, if detrial and error it is a comparatively simple matsired, may provide a time constant such as to ter to determine the minimum distance between contribute to the frequency of pulse oscillation. earth connections for a particular range of com- The left hand portion of tube 2l constitutes munication. Generally speaking, the further the generator side, while the right hand portion apart the two ground connections of the transof tube 2l is the amplier side for the pulses promitter and receiver are placed, the greater will duced in the generator side. Tube 22 is an be the distance range of communication, within ampliiier which ampliies the output from the certain limits. The term ground or earth conamplifier side of tube 2l. The output from nections used herein is not limited to a con- 25 amplifier 22 is passed through transformer T3 necticn in the soil, since the electrodes for the to the ground connections E, E. The primary transmitter and the receiver can be located in and secondary windings of transformer T3 are water, such as in a lake, or in the ocean for adjustable, as shown, to obtain the proper imcommunication between two ships, or between pedance match to the connecting circuits. a ship (or a submarine) and a shore station. It In the operation of the system of Fig. l, the will be apparent that when the spaced electrodes oscillator electrode structure of tube 2l receives are inserted in the ground or in the water, the anode potential by the charging of condenser effectiveness of the system may vary with the C1 through resistance Ri. When the anode poresistance of the earth or the water. There is, tential rises high enough, anode current starts, however, a compensating effect in respect to the causing transformer T2 to push the oscillator eiect of ground resistivity, because signals and control electrode momentarily positive, thereby noise tend to be inuenced alike, leaving their causing a rapid discharging of condenser C1 and ratios more or less alike, except for conditions a charging of condenser Cz. The anode curwhere receiver noise limits the range of comrent then cuts off, leaving the anode potential munication. low and control electrode bias .potential high.

The communication system of the invention, Then, after a time, the bias potential decreases employing short high-power pulses, has both by leakage of charge from condenser C2 through military and civilian uses and :possesses the folresistance R2, while the anode potential rises by lowing advantages among others: (l) A higher charging of condenser C1 through resistance R1, peak DOWSI Can be TanSnlf/ed than obtainable ending in another pulse 0f anode and grid Cul; by me Customary type 0f Continuous Waffe 45 rent. This process repeated at rapid intervals ,transmtte equlpment; Q the System Gf me (say at a rate of 20,000 pulses per second, with the mveltlon 1S Very hard to mterfelswlth. coflsbe' pulses very short compared to the time intervals quemly the piocedule known as Jammmg y between them) provides the pulse oscillation. an enemy 1n time of war has reduced effect, and T d l t th f th 1 (3) by making the receiver of the invention op- 50 O m0 u a e je nequeny e pu se OSCI" crate synchronously with the transmitter, or by latlon a' modulatmg potentlal 1S apphef through using an adjustable threshold system in additransformer Tl and the parallel combination of tion to limiting, it is possible to receive transresistance R2 and condenser C2. This causes a mitted pu1se signals despite extraneous and unvariation or modulation in the oscillator grid desirable earth potentials. bias potential which causes anode current to 3 start at variable time intervals following preceding pulses and thereby modulates the pulse frequency.

The modulation may, as an example, comprise voice frequencies ranging from say 150 to 3000 cycles per second, and may be of such an amplitude as to modulate the pulse frequency by a maximum of plus and minus 3000 to 6000 cycles per second.

The frequency modulated pulses are amplified in the amplifier portion of tube 2l and again in tube 22 from which relatively high power pulses are delivered to the spaced ground connections E, E through impedance adjusting transformer T3.

At the receiver of Fig. 2, pulse power picked up by the spaced ground connections is amplified in push-pull pulse amplifier 23 and applied to a frequency selective circuit 34 tuned to the mean pulse frequency but broad enough 1n response to respond to the frequency modulation of the pulses. Energy from the tuned circuit is again amplified and limited to nearly constantJ value in amplifier 24. The limiting is accomplished largely by virtue of automatic control electrode bias which increases With increasing input, supplied by resistance R shunted by condenser Cs. The resistance and condenser are so chosen as not to respond much to frequencies above the lowest modulation frequency.

Output from amplifier 24 is then applied to a frequency modulation detector comprised of discriminator circuit 25 and push-pull demodulator tube 2S. Modulation frequency output from demodulator 2E is amplified in audio amplifier 21 and passed on to headphones 2B through a coupling transformer 29.

In order to prevent or reduce the probability that noise and interference arriving at the receiver between the arrivals of the signal pulses may be heard in the headphones, I provide a feed back path through condenser' C@ to the control electrode bias resistor Rs. As a result of this feed back, the sensitivity or ampliiicaticn of vacuum tube 2-3 is modulated by the output alternating current potential of tube 24 in such a direction as to make the amplilication maximum when a signal pulse is due to arrive but to make it a lower value for all other time periods between pulses This is not regeneration of the signal in the ordinary sense since, due to the balanced arrangement of the circuits associated with tube 23, the energy fed back is not reamplied.

In operation, the receiving system may be designed and adjusted for` a fixed overall gain, or total aznplication, and the output signal strength may be controlled by adjustment of the resistance across the primary winding of the receiver input transformer. This tecomponents in correct relative adjustment and is an aid to standardization.

The transmitter and receiver of both the systems of Figs. l and 2 use the same set of ground connections if a switch or relay is provided to connect the ground leads with the transmitter for talking and with the receiver for listen-- ing.

The pulse length modulated signals may be received with the receiver of Fig. 2 if the frequency modulation detector shown there is replaced by an amplitude modulation detector and the amplifier 2f; is made to operate without limiting. By the application of threshold and limiting effects in the pulse amplifiers, before the pulses are integrated in a frequency selective circuit, it

is possible to eliminate substantially all effects of noise and interference so long as the pulse amplitude is more than twice the peak amplitude of the noise and interference and the threshold and limiting amplifier is adjusted so that the transition from no response to full response takes place at inputs about equal to half the pulse amplitude.

Where Water is used to replace the soll for a ground, as in the case where the transmitter Would be located on a submarine, the tvvo ground electrodes will, of course, be spaced far apart, as in the case when actual soil is employed for ground. The submarine hull can constitute one electrode, while another electrode can be located at the end of a long insulated conductor run out from the submarine.

What is claimed is:

l. A pulse receiving system comprising a pushpull amplier, an input circuit supplying to said amplifier pulses whose time of occurrence is modulated, said input circuit including a pair of -spaced ground connections for receiving the pulses transmitted from a remote point a pulse frequency selective circuit in the output of said amplifier, a limiter coupled to said selective circuit, and a pulse frequency modulation detector coupled to the output of said limiter.

2. A pulse receiving system comprising an amplifier, an input circuit coupled to said amplifier for supplying said amplifier' with pulses Whose time of occurrence is modulated, a selective circuit tuned to the mean pulse frequency but broad enough to respond to the modulation of the pulses coupled to the output of said amplifier, an amplitude limiting amplifier coupled to said selective circuit, said limiting amplifier comprising a gridcontrolled vacuum tube and a demodulator including a discriminator circuit coupled to the output of said amplitude limiting amplifier.

3. A receiving system for pulses Whose frequency is modulated, comprising an amplifier, a input circuit coupled to said amplier for supplying said amplifier with pulses whose frequency is modulated, a selective circuit tuned to the mean pulse frequency but broad enough to respond to the modulation of the pulses coupled to the output of said amplier, an amplitude limiting gridcontrolled amplifier vacuum tube coupled to said selective circuit, a `fgequency modulation detector including a discriminator circuit coupled to the output of said amplitude limiting amplifier, and a push-pull connected demodulator tube coupled to said discriminator circuit.

4. A pulse receiving system comprising an amplier, an input circuit coupled to said amplifier for supplying said amplifier with pulses Whose time of occurrence is modulated, a pulse frequency selective circuit in the output of said amplifier, an amplitude limiter coupled to said selective circuit, a pulse frequency modulation detector coupled to the output of said limiter, and a feed back circuit from the output of said amplitude limiter to the input of said amplifier for controlling the sensitivity of said amplifier.

5. A pulse receiving system comprising an amplifier, an input circuit coupled to said amplifier for supplying said amplier with pulses whose time of occurrence is modulated, a selective circuit'tuned to the mean pulse frequency but broad enough to respond to the modulation of the pulses coupled to the output of said amplifier, an amplitude limiting amplifier coupled to said selective circuit, a demodulator including a discriminator circuit coupled to the output of said amplitude limiting amplifier, and a feed back circuit from the output of said amplitude limiting amplifier to the input of said first amplifier for controlling the sensitivity of said first amplifier.

6. A pulse receiving systm comprising an amplifier, an input transformer having a secondary winding coupled to said amplifier and a primary winding coupled to a source of pulses, a variable resistor across the primary Winding of said transformer, a pulse frequency selective circuit in the output of said amplifier, an amplitude limiter coupled to said selective circuit, a detector coupled to the output of said limiter, and a feed back circuit from the output of said limiter to the input of said amplifier.

7. The method of operating a pulse receiver which comprises receiving time modulated pulses, amplifying the received pulses, limiting the amplified pulses, demodulating the amplified-limited pulses, and feeding back amplified energy, prior to demodulation, from one portion of said receiver to a preceding portion in such sense as to reduce the gain during intervals between received pulses.

8. A receiving system for pulses whose frequency is modulated, comprising an amplifier, an input circuit coupled to said amplifier for supplying said amplifier with pulses whose frequency is modulated, a selective circuit tuned to the mean pulse frequency but broad enough to respond `to the modulation of the pulses coupled to the output of said amplifier, an amplitude limiting gridcontrolled amplifier vacuum tube coupled to said selective circuit, said limiting amplifier having a parallel combination of condenser and resistor for automatically controlling the bias on said grid, the values of said resistor and condenser heing so chosen that they do not respond much to frequencies above the lowest modulation frequency, a frequency modulation detector including a discriminator circuit coupled to the output of said amplitude limiting amplifier, and a pushpull connected demodulator tube coupled to said discriminator circuit.

CLARENCE W. HANSELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,262,406 Rath Nov. 11, 1941 2,363,651 Crosby Nov. 28, 1944 

